Cardiovascular and cerebrovascular diseases have high incidence rate, high disability rate, high mortality rate, high recurrence rate and many complications, which seriously threatening people's health and quality of life. Thrombosis is one of the major causes of cardiovascular and cerebrovascular diseases. Antithrombotic drugs including anticoagulants are the first-line drugs in clinical for the treatment of cardiovascular diseases, and occupy an important position in the medicine market. The anticoagulant drugs mainly include coumarin anticoagulants and heparin anticoagulants, which have definite pharmacodynamical effect and pharmacological mechanism, but also have obvious clinical application defects: the defects of the anticoagulant drugs include severe bleeding tendency, slow onset and large individual differences due to their inhibition of synthesis of series of coagulation factors; heparin mainly target at the coagulation factors IIa and Xa (f.IIa, f.Xa) in the common pathway of the coagulation cascade, and the major defects of the drugs are serious bleeding risk and thrombocytopenia associated with their targets. Therefore, a new type anticoagulant drug, which has an advantage on pharmacological and pharmacodynamic action, is needed for clinical. The core of developing a new type anticoagulant drug is to avoid bleeding tendency efficiently; however, a breakthrough progress has not been made in the research of the innovative drugs with low bleeding tendency.
Fucosylated glycosaminoglycan (FGAG) from an echinoderm is a glycosaminoglycan derivative having fucose-substituted side chains. It has a chondroitin sulfate-like main chain composed of glucuronic acid (GlcUA) and acetyl galactosamine (GalNAc), and has fucose (L-fuc) side chains that are attached to the glucuronosyls of the main chain via α-1,3 glycosidic bonds. Both the hydroxyl groups of polysaccharides on the main chains and the side chains have different degrees of sulfation (J. Biol. Chem., 1996, 271: 23973-23984; Mar. Drugs, 2013, 11: 399-417). Native FGAG has strong anticoagulant activity (Thromb. Haemost., 2008, 100: 420-428; J. Biol. Chem., 1996, 271: 23973-23984).
However, native FGAG still has extensive and contradictory pharmacological effects, including induction of platelet aggregation, bleeding tendency and activation of factor XII, etc (Thromb. Haemost., 1988, 59: 432-434; Thromb. Haemost., 1997, 65 (4): 369-373; Thromb. Haemost., 2010, 103: 994-1004). Depolymerized FGAG after appropriate depolymerization may retain the anticoagulant activity of native FGAG and reduce the platelet activating activity (Thromb. Haemost., 1991, 65: 369-373). China patents CN101724086B and CN101735336B disclose a method for preparing depolymerized FGAG, in which depolymerized FGAG is obtained by hydrogen peroxide depolymerization of FGAG, and the resultant products significantly decrease the bleeding tendency.
Since FGAG is a glycosaminoglycan derivative with large molecular weight and complex structure, on the premise of reducing the side effects while retaining the pharmacological activities, it is very difficult in technique to achieve depolymerization that can be effectively controlled in process to obtain a low molecular weight derivative with a characteristic terminal structure. Considering that the hydrogen peroxide depolymerization method lacks of selectivity toward glycosidic bond and the process control is complex, the present invention establishes a new method for depolymerization of FGAG—deacetylation deaminative depolymerization method. In this method, FGAG is first treated with hydrazine to subject D-2-(N-acetyl)amino-2-deoxygalactose (D-GalNAc) to partial deacetylation, to obtain partially deacetylated products of FGAG containing D-2-amino-2-deoxygalactosyl (D-GalNH2); followed by treatment with nitrous acid and subjected to deaminative depolymerization to obtain depolymerized products of FGAG containing terminal 2,5-anhydrated talose or its reduced derivatives. In the prior art, FGAG depolymerization method by deacetylation and deamination has not been reported, and low-molecular-weight fucosylated glycosaminoglycan containing a terminal 2,5-anhydrated talose or its reduced derivatives has not been reported either.